Pyrogallic Acid

Pyrogallic acid (Pyrogallolum, Acidum pyrogallicum, Trioxybenzol), trioxyphenol of formula C₆H₃(OH)₃ [1,2,3]. Discovered at the end of the 18th century by Scheele. P. consists of light, colorless, brilliant, elongated, thin crystalline needles or plates (flakes) with a melting point of 131-133.5°, odorless, with a strongly bitter taste. Well soluble in water (1:1.7), alcohol (1:1.3), ether (1:1.5), poorly soluble in carbon disulfide (CS₂), chloroform, benzene. The aqueous solution is colorless, with a very weak reaction; when standing in air, it gradually becomes acidic and at the same time turns yellow, brown, or dark brown. Pyrogallic acid is a strong reducing agent. Due to its reducing properties, P. is used for determining oxygen in the analysis of gas mixtures, in photography as a developer, and in cosmetics as a hair dye. Action on protein and microorganisms. P. gives precipitates with protein solutions, poorly soluble in water and easily soluble in excess protein solutions or upon the addition of soda. The antiseptic and deodorant properties of P., used in medicine, are also confirmed by experimental data—thus, animal tissues can be preserved for months in a 1-1¹/₂% solution of P. without the development of bacteria and odor, 2-2¹/₂% solutions quickly kill putrefactive bacteria and destroy the foul odor of decaying masses. Local action. When used in the form of ointments on wounds, mucous membranes, and damaged skin, P. has a slight irritating effect; only with vigorous rubbing or with prolonged use can erythema and dermatitis be observed. When P. is used, the skin is colored brown or black by oxidation products of P. Absorption of P. occurs very easily even through intact skin, therefore to avoid poisoning it should not be applied to large surfaces and more than 5.0 per day. P. is excreted by the kidneys partly in unchanged form, partly in the form of paired sulfuric acids, and partly in the form of unknown oxidized products that color the urine dark green, dark brown, or almost black. Excretion of small amounts occurs quickly. Resorptive action. The main changes produced by P. concern the blood: erythrocytes shrink, become angular, and lose their pale part of their Hb, which passes into the plasma and turns into methemoglobin. In the blood in large quantities appear fragments of erythrocytes and their "shadows." The blood becomes liquid, chocolate-brown in color. With a slower course of poisoning, jaundice occurs and Hb and methemoglobin are excreted in the urine. The amount of oxygen in the blood sharply decreases. Fragments of erythrocytes can form homogeneous masses, which lead to vascular obstruction. All these phenomena can explain the observed degenerative changes in parenchymal organs and numerous hemorrhages in poisoning. In the kidneys, phenomena of acute hemorrhagic nephritis are observed. In the striated muscle, disappearance of longitudinal and transverse striation and often the appearance of granularity can be observed; the heart muscle also loses its normal structure. Changes in the central nervous system can hardly be considered as a direct action of P. Symptoms of acute poisoning: headache, diarrhea, vomiting, muscle tremors, weak pulse, prostration, dark urine, containing protein, blood, Hb breakdown products, sometimes sugar. In rapidly developing cases—cyanosis, shortness of breath, convulsions, collapse; at the end of poisoning—anuria, picture of uremic coma, after which death quickly follows from paralysis of the central nervous system. The lethal dose for humans has not been precisely established. In one case, 15.0 P. orally gave, despite vomiting, a fatal outcome, while in another case 8.0 P. caused only transient poisoning. Treatment of acute poisoning is purely symptomatic (stimulants, cardiac agents, etc.). With external application, the ointment from P. should be quickly removed with alcohol and ether. When taken internally—stomach washing should be done as soon as possible, then to hinder absorption, Carbo animalis 20-30 g every 2 hours in aqueous suspension, or 100-200 cm³ of oil (olive, almond, sunflower, etc.) or Calcaria saccharata (Calcii oxydati hydrati 5.0, Sacchari 15.0, Aq. dest. 50.0. M. D. S. no 1 tablespoon every 5 minutes); Natrium sulfurosum (10.0 in 200.0 water, a tablespoon every 2 hours) is also recommended internally with the expectation of chemical neutralization of the poison. Application. P. is used as an antiseptic and keratoplastic agent mainly in the form of ointment (5-10%), more rarely as a 1-2% alcoholic solution for various skin diseases (psoriasis, lupus, favus, herpes tonsurans, eczema marginatum, chronic eczema, etc.). As an example, one can cite the prescription of the so-called Ung. Pyrogalloli compositum Unna: Pyrogalloli 5.0, Acidi salicylici 2.0, Ammonii sulfoichthyolici 5.0, Vaselini flavi 88.0. M. f. ung. D. S. Ointment. When using P., it is necessary to examine the urine of patients daily and immediately stop treatment with it if the urine becomes pink or black. In aqueous solutions, P. is used as a relatively harmless agent for dyeing hair brown, and together with an ammonia solution of silver nitrate—for dyeing black; additionally, in a 1-3% aqueous solution, P. is used for foul-smelling rhinitis (ozaena) and foul-smelling ulcers (e.g., cancerous) as a deodorant. Due to the high toxicity of P., its preparations are not used internally. P. is stored in a well-closed glass vessel, protected from light. Preparations. 1. Pyrogallolum—see above. 2. Pyrogallolum oxidatum (Pyraloxin Unna)—a product of oxidation of P. in an alkaline environment; black-brown powder, soluble in water. Used, P. 3. Eugallol (factory Knoll) C₆H₃(OH)₂O.OCCH₃ (Pyrogallolum monoaceticum), represents a solution of 2 parts of monoacetate of P. in 1 part of acetone. A syrupy yellow-brown mass, easily soluble in water. Used in the same cases as P., in 1-10% ointments and pastes, as well as in pure form or dissolved in double the amount of acetone for lubrication—after ¹/₂ hour it dries and forms a film similar to lacquer; it is dusted with zinc oxide or covered with zinc ointment. Avoid lubricating healthy skin. 4. Lenigallol (factory Knoll) C₆H₃(O.OCCH₃)₃ (Pyrogallicum triaceticum), white powder, insoluble in water. Used mainly for eczema in the form of 0.5-5% ointment or paste, especially in children. Does not have an irritating effect, does not stain linen, acts weaker than P. Has no effect on healthy skin. In stronger ointments (10-30%)—against psoriasis. 5. Saligallol. (Pyrogallolum disalicylicum) is used for skin diseases in the form of solutions in chloroform and acetone (1:19). 6. Gallacetophenone, CH₃CO.C₆H₂(OH)₃, trioxyacetophenone, a product of condensation of P. and acetic acid. A dirty-colored crystalline powder, soluble in 600 parts water, easily soluble in hot water, alcohol, glycerin, and ether. Used, like P., for skin diseases in 5-10% ointments or solutions.

M. Nikolaev. Discovery in court cases. Objects of research can be parts of internal organs, urine, and hair dyes. The skin under the action of P. is colored dark brown. The urine of persons poisoned with P. has a dark brown color. P. is not volatile with steam and is extracted from an acidified solution with ether or chloroform. Reactions: 1) when mixed with solutions of caustic alkalis, P. gives a brownish coloration, then blackening; 2) ferric chloride gives with P. a red coloration, which passes from calcium carbonate to blue.